Researchers overcome important hurdle in quest to make high-frequency signals practical

Terahertz data links, which researchers tested on the University’s campus, could increase rate of data transfer. The innovation could significantly increase the speed of wireless networks.

The frequency range found between microwave and infrared radiation could be a key player in the next generation of wireless communication. For the first time, University researchers have demonstrated that these “terahertz” frequencies can be reflected off walls and still transmit data precisely, an important early step in the development of this new technology.

Terahertz data links could increase data transfer by a factor of more than a thousand compared with existing wireless technology, said Daniel Mittleman, professor of engineering and senior author of the study, which was published in APL Photonics.

Terahertz communication occurs at frequencies above 95 gigahertz, said Jianjun Ma, postdoctoral research associate and co-author of the study. Its use offers dramatically faster transfer speeds than does current wireless technology such as Wi-Fi routers, which operate in the microwave range of only a few gigahertz, Ma said.

There are many obstacles to the widespread adoption of terahertz technology. Traditional microwaves broadcast in all directions from a transmitter, but terahertz signals must travel in a single direction, requiring the transmitter to point directly at the receiver, Mittleman said.

Furthermore, terahertz signals are unable to travel through or around objects that disrupt their line of sight. “We have to find a way to go around blockages,” Mittleman said.

Mittleman’s goal was to determine whether terahertz signals could bounce off walls in order to bypass disruptions while still transferring data accurately. To study this, Mittleman’s team set up devices capable of transmitting and receiving terahertz frequencies and then reflected the signals off walls of a variety of materials. They measured the number of “ones and zeroes” received and calculated the “bit-error-rate,” the number of incorrect transfers made per bits sent, Mittleman said. The researchers found that even bouncing the signal off two walls — around a corner in Barus and Holley — resulted in a bit-error-rate of one in a billion. “It’s way better than your phone actually does,” Mittleman said.

The researchers also tested the technology outdoors, a task that required a special license from the Federal Communications Commission. Any outdoors tests above 100 gigahertz require such a license to ensure they do not interfere with satellites, Mittleman said. He hopes the FCC will start paying more attention to terahertz technology.

Generating signals with enough power at terahertz frequencies poses another technical hurdle to its usage as a means of data communication. “We proved that even though it was reflected by the wall two times, we still had enough power to keep the data link,” Ma said.

It remains unclear how many bounces might be possible for a practical terahertz data link, Mittleman said, adding that this was a first demonstration and more research can be done to determine the technology’s limits.

Aside from being studied as a mode of wireless communication, terahertz waves have been examined for various other purposes, said Rajind Mendis, assistant research professor of engineering, who has studied the technology for nearly two decades.

According to Mendis, terahertz waves can penetrate certain substances, including cardboard, paper and ceramics. For this reason, they are used in detection of explosives and illicit drugs, food quality control, preservation of historical artwork and diagnoses of certain cancers, Mendis said.

Mendis believes that terahertz signals will eventually become part of the next generation of wireless data transfer. “It is inevitable that we are moving towards the terahertz range for communications,” Mendis said.

While higher-frequency radiation, such as X-rays, poses some risk to humans, terahertz waves are not harmful at all, Mendis said.

Mittleman is skeptical that terahertz-range frequencies could replace current 4G or future 5G cell networks, but he believes the technology could be used in many other cases. He envisioned someone stopping by a kiosk in an airport and being able to download a high-definition movie to their phone in a matter of seconds, or a data center using the technology to route data wirelessly.

Mittleman, Ma and Mendis all noted that with the interconnectedness of devices on the “Internet of Things,” the use of terahertz frequencies could prevent such devices from clogging existing wireless networks, making them faster.